Heat exchangers are often used in high performance environments and are subsequently required to perform within very high tolerances. Such high performance heat exchangers may need to be compact, and hence may comprise precision made fluid channels for flow of cooling fluid. However, defects within the heat exchanger or cooling channel may be formed during manufacture, particularly during joining on the constituent pieces of the heat exchanger. Such defects can result in a loss of system integrity, a loss of efficiency, or total system failure, for example by leakage of cooling fluid during service. Therefore, the quality of joints within such heat exchangers is of paramount importance.
Fluid-cooled cold plates are an example of high-performance heat exchangers, and are designed for use in very high power applications where space is at a premium. Manufacture of cold plates typically combines two techniques: machining and vacuum brazing. Firstly, a fluid flow channel defining at least a part of a cooling circuit through the cold plate is machined into at least one plate. Then the machined plate is vacuum brazed to another plate. The machined fluid flow channel may be designed specifically for the chosen application of the cold plate, and may be optimised according to the power and configuration of components to be cooled by the cool plate. Therefore, the positioning of the brazed joints within the cold plate may be determined on a case by case basis and can vary from a simple channel to a complicated circuit (e.g. for high power requirements).
Quality inspection of joints within cold plates, such as brazed joints on internal surfaces, is notoriously difficult and since the joints are internal to the cold plate, straightforward (e.g. visual) inspection of them may be impossible. Moreover, determining the precise location of the joints within the cold plate can be problematic. Conventional methods of inspection include the use of ultrasonic sensors. However, such sensors can be unreliable for various reasons, including a lack of depth penetration through the plate, as well as because of data resolution issues. Further, a coupling fluid needs to be applied to the cold plate to transmit the ultrasonic vibrations from the sensor to the cold plate and back, and hence the cold plate often requires additional cleaning after quality control inspection, thereby increasing the costs of quality control. Because of the various constraints of conventional ultrasound inspection, it is often a manual process carried out by hand. This can make the process slow and susceptible to human error.
Therefore a reliable, efficient, dynamic, and robust inspection method for inspection of joint integrity of heat exchangers is required to help ensure the quality of the heat exchanger after manufacture.